1. Field of the Invention
The present invention relates to a sheet conveying apparatus including a mechanism which corrects a skew feed of a sheet, and an image forming apparatus including the same.
2. Description of the Related Art
In general, for an image forming apparatus, an image recording position with respect to a sheet position is an important factor of image quality. Therefore, for a conventional image forming apparatus, various kinds of mechanisms to be mounted thereon for correcting a skew feed of a sheet are proposed in order to improve their recording accuracy.
For example, there is known a sheet conveying apparatus which is provided with, on an upstream side (hereinafter, referred to as “upstream side”) in a sheet conveying direction which is closest to an image forming portion, a registration roller pair extending in a width direction perpendicular to the sheet conveying direction, and a shutter member (Japanese Patent Application Laid-Open No. H09-183539). The sheet conveying apparatus adopts a registration shutter method in which a skew feed of a sheet is corrected by bringing the leading edge of the sheet into abutment against the shutter member. The above-mentioned shutter member is configured to be swingable about the rotational axis of the registration roller pair into a posture allowing latching of a leading edge of a sheet through abutment against the leading edge of the sheet, and into a posture allowing a sheet to pass therethrough. The shutter member is urged by an elastic member, such as a spring, in a direction for restoring the shutter member, after a sheet has passed the shutter member, from the posture allowing a sheet to pass the shutter member to the posture allowing latching of a leading edge of a sheet.
That is, in the sheet conveying apparatus, on a rotational shaft of a conveying rotatable member of the registration roller pair, the shutter members are pivotably disposed at predetermined intervals along the axial direction of the rotational shaft so that a leading edge of a sheet, which is conveyed by a conveying roller pair on an upstream side, is brought into abutment against abutment surfaces of the shutter members. Then, a loop is gradually formed on the sheet so as to increase a force for pressing the shutter members by the leading edge of the sheet. Therefore, the shutter members are pressed to be pivoted and retracted to allow the sheet to pass through the shutter members. When the leading edge of the sheet is pressed against the shutter members to pivot the shutter members, the leading edge of the sheet is oriented along the abutment surfaces of the shutter members so that the leading edge of the sheet is aligned with a direction perpendicular to the sheet conveying direction. In this state, the registration roller pair conveys the sheet. Thus, the skew feed of the sheet is corrected during the conveyance of the sheet.
However, in the conventional sheet conveying apparatus described above, when a sheet is conveyed through the registration roller pair, the shutter members are urged by an elastic member such as a spring for restoring the shutter members to the posture allowing latching of the leading edge of the sheet, and hence the shutter members are pressed against the surface of the sheet which is being conveyed by the registration roller pair. As a result, for an extremely thin sheet having a basis weight of less than 60 g/m2, or a sheet having a low stiffness, such sheet is brought into a corrugated state due to the pressing force of the shutter members which are disposed in the axial direction at predetermined intervals. Accordingly, when the sheet in the corrugated state is nipped by a transfer roller portion (transfer portion) of the image forming portion on a downstream side, the sheet of paper may be crinkled.